The present invention relates to manually operated circuit breakers and, more particularly, to circuit breakers having a movable contact on a spring biased contact member manually actuated through a toggle arrangement and automatically tripped by an overcurrent responsive mechanism.
The use of fuses has been declining in recent years due to circuit breakers which provide reusable electrical circuit protection. Circuit breakers enable an electrical circuit to be protected from a multitude of overcurrent and short-circuit situations with a manual resetting of the breaker rather than replacement of a fuse element. Generally, circuit breakers provide an exterior handle for manual opening and closing of the breaker which operates a pair of electrical contacts through a toggle arrangement, such as an overcenter linkage.
While the contacts are engaged to thus complete an electrical circuit it is important that sufficient pressure be applied to maintain engagement of the contacts and avoid arcing of the contact material. Further it has been found to be advantageous for the circuit breaker to operate quickly, in a snap-type action, during both opening and closing of the breaker in order to minimize the time during which arcing could occur. The contact pair consists of a stationary contact and a movable contact which may be attached to one end of a pivotally mounted contact member. If the pivoting mount for the contact member is a fixed position mount, wear of the contact due to arcing will result in lessening of the pressure between the two contacts. For this reason, overtravel of the movable contact is generally utilized to provide a wider tolerance range for engagement of the contact pair. In addition, it has been found that arcing of the contact pair may be diminished by providing a wiping action between the contacts as closing occurs.
Automatic circuit breakers include a mechanism for sensing overcurrent conditions as well as short-circuit conditions at current levels for which the appropriate breaker would be used. Any one of a number of known mechanisms for providing both overcurrent protection and short-circuit protection may be used in an automatic circuit breaker. When the circuit breaker automatically opens due to either over-current or short-circuit detection, it is desired that the physical opening of the contacts occur at as rapid a rate as possible to avoid arcing of the contact pair. In order to obtain the rapid opening of the contacts, mechanical mechanisms such as springs are often provided between the stationary and movable contacts. While the opening of the circuit breaker occurs at a speed dependent upon the force of the biasing spring provided between the contacts, manual closing of the breaker is likewise effected by this spring pressure.
U.S. Pat. Nos. 3,581,261 and 3,610,856 are illustrative of automatic circuit breakers which address all of the above noted problems. In each of these references, overtravel of the movable contact member is provided by a pivotal mount for the contact member. A helical coil spring extends through an aperture in the contact member and is mounted at either end in the circuit breaker case. During a majority of its use, the circuit breaker is in a closed condition, and thus the helical coil spring would be deflected. Fatigue of the coil spring, to any degree, lessens the tolerance range of the movable contact due to overtravel.
U.S. Pat. Nos. 2,876,308 and 3,101,399 illustrate circuit breakers using a solid pivot mount for a movable contact member with an elongated opening in the contact member. In each of these patents, the contact member is biased by a coil spring to one extreme of the elongated opening in the contact member. The tortuous path of the coil spring in each of these references can subject the spring to fatigue over an extended period of time.
A number of circuit breaker designs have been proposed including leaf-type springs for biasing movement of a pivotally mounted contact arm. U.S. Pat. No. 2,681,396 at FIGS. 27 through 36 illustrates a contact arm pivotally mounted within an elongated opening in a case structure of the breaker. The pivot, and thus contact arm, are normally biased toward an upper end of the elongated opening by reason of a bent leaf spring positioned between the pivot and a portion of the case structure. This leaf spring arrangement would present difficulties in assembly since the spring would be in a stressed condition while assembly was undertaken. Also, movement of the movable contact member is limited by the spring acting between the contact member and the breaker case.
U.S. Pat. No. 2,810,048 illustrates a circuit breaker having a contact arm pivotally mounted within a case. In this instance, the pivot is fixed in the case while the contact arm has an elongated hole through which the pivot supports the arm. A leaf-type spring, providing the only biasing for the linkage arrangement of the circuit breaker, is positioned between the actuating handle and a point on the contact arm. This spring acts both to bias the contacts to an open condition as well as support the contact arm in a raised position relative to the fixed pivot when the breaker is in an open condition.
U.S. Pat. No. 3,500,275 provides a leaf-type spring biasing a contact arm toward an upper end of an elongated pivotal mount. The leaf spring cooperates with a compression coil spring and, in fact, is operatively connected to the compression coil spring between the actuation handle and the contact arm. This arrangement of springs could present problems in assembly due to the multiple springs needing to be compressed for and during assembly.